INFO About JDK1.6

Hi ,
This is Ravi, i am using the jdk1.5 version thats working fine, i will change the my jdkversion to jdk1.6 in Eclipse and JRE also jre6 ,but compilation time i have error
'enum' should not be used as an identifier, since it is a reserved keyword from source level 5.0 , in using jdk1.6
how to resolve that error,please replay as soon as possible